Method and apparatus for preventing excess pressure increase in steam generators with low water content



y 1939- o. H. HARTMANN El AL 2,167,

IETHOD AND APPARATUS FOR PREVENTING EXCESS PRESSURE INCREASE IN STEAK GENERATORS WITH LOW WATER CONTENT Filed Sept. 22. 1936 2.4 momma 1.0mm Wren/0r;

Attorneys Patented July 25,1939

PATENT OFFICE METHOD AND APPARATUS FOR PREVENT- ING EXCESS PRESSURE INCREASE IN STEAM GENERATORS WITH LOW WATER CONTENT Otto H. Hartmann and Rudolf Loewenstein, Kassel-Wilhelmshohe, Germany, assignors to the firm Schmidtsche Heissdampf, Gesellschaft m. b. H., Kassel-Wilhelmshohe, Germany Application September 22, 1936, Serial No. 102,030

' In Germany October .19, 1935 10 Claims. (Cl. 12235) The invention relates to steam generators, and particularly to those of small water content.

In steam generators with .a small water content, for examplesteam generators or the like for driving vehicles which are capable of rapid generation of steam, particularly those provided with a grate for supplying heat, it is necessary to provide some means 'of preventing the pressure of the steam in the generator from rising to an excessive degree, when the withdrawal of steam is reduced or adjusted, as when the vehicle is suddenly brought to a stop. When the vehicle passes from rapid motion to a stop, the grate still contains a considerable amount of incandescent coal, which itself can radiate a large amount of heat, even when the boiler draft is'cut off. In such small steam generators with low water content and small steam chambers, the pressure of the steam therefore rises abruptly, after the steam withdrawal passage is closed, because of the continued generation of steam by this radiated heat. blown off atthe proper times, considerable Water losses result; while if use is made of a closed circuit for the engine drive, impractically large "quantities of additional water are required. On

the other hand, if the safety valve fails to operate or is adjusted to 'a very high blow-ofi pressure; to avoid such loss, the resulting excessively v high pressure of the steam may exert too great a strain on the construction material and cause the pipes to burst.

' The procedure often used in other types ofsteam generators for reducing the excessively high pressure of passing additional cold water into the boiler tubes cannot be used in rapid steam generators with low water content and small steam chambers; on the contrary, as applicants experience has demonstrated, the pressure increases, by reason of the reduction of the available space in the steam chamber caused by the additional feed, much more rapidly than without such feed.

This defect'is eliminated by the present in-- Therefore, when the safety valve is subdivided Water supplied the pressure increase can be kept within permissible limits; the variations in pressure may even be controlled as desired. The safety valve is adjusted to a somewhat higher pressure than for ordinary operation, for the purpose of producing a certain additional reservoir action of the boiler. The water can be introduced into the container, for example, by means of a spray device with a suitable number of smalldischarge openings to subdivide the water finely, or by means of trickling surfaces built in the steam chamber of the reservoir, or both methods may be used together to improve the operation of the process.

Further objects and advantages of the invention will appear more fully from the following description, particularly when taken in conjunction with the accompanying drawing which forms a part thereof.

Fig. 1 is a diagram of the result obtained in experiments showing the effect of the method and apparatus in reducing the steam pressure when the steam take-off is closed in a quick vaporizer embodying the invention.

Figs. 2A are simplified diagrammatic views of three different embodiments of apparatus for carrying out the process of the invention.

In Fig. l the steam pressures are expressed in atmospheres (excess pressure) on the ordinate axis and the injection periods in minutes on the abscissa axis. The upper curve a; shows the pressure increase of the steam when the steam take-off is closed without spraying in water to precipitate the excess steam. The normal operating pressure is maintained at 40 atmospheres. As shown on the drawing, the pressure rises considerably in a very short time after closing the steamdelivery or take-off valve, for example, after one minute it has increased to 65 atmospheres, .and after three minutes to 80 atmospheres. Curve 1) shows the varying pressures of the steam when use is made of an arrangement according to the present invention, in which a predetermined quantity of water, for example about 5 kg., is sprayed into the steam chamber of the reservoir for an interval of 2 minutes. The spraying begins after about minute. This period of delay can, of course, be materially shortened, or spraying may begin almost simultaneously with the closure of the steam delivery. As shown on the diagram, the steam pressure first rises for a short time above 40 atmospheres, as on the curve a. The further pressure increase over interval at is not so abrupt, through the action of the water sprayed in, by condensing the steam while at the same time itself being heated approximately to boiler temperature, and the pressure increase ceases in the second half of the interval d, at the end of which the water spraying is stopped. The steam pressure rises. again, of course but, as shown on Fig. 1, not nearly to the same extent as on curve a without spraying of water. The third curve c shows the variation in pressure of the steam with approximately double the quantity of water sprayed in as compared with curve b, and a spraying interval twice that of b and shown by line e. After the pressure increase of the steam has ceased after about 1 minutes, in this case it drops to the end of interval 6, when the feed of water to the steam chamber of the reservoir is cut off. From this moment on the steam pressure again rises, but not to the same extent as in the curve a or even in the curve b. In general, the second part of the pressure increase is no longer important because, with a vehicle boiler for example, normal operation has again been resumed. The dotted curve f shows the pressure increase without preciptiation of the excess steam.

These experiments thus show the advantageous operation of the present invention by utilizing the condensation of the steam effected by means of trickling surfaces or finely subdivided water dispersed by means of spray nozzles or the like.

Similar parts are designated by similar reference characters in Figs. 2-4.

The feed water is supplied to the tube boiler or vaporizer I from a reservoir 2 by a feed pump 3, preferably constructed as a piston pump, by pipe I I and through a preheater 4 heated in any suitable manner. The steam generated in the tube I passes to the point of consumption through a passage 5 provided in the usual manner with a safety valve 6 and a delivery or take-off valve '5. Branching off from steam pipe 5 (Fig. 2), or from some other part of the steam line in front of the valve 1, is a pipe 8 which passes to the container or reservoir 9 forming a steam chamber into which a spray II? empties. Feed water is supplied to the spray II] from the pressure pipe I I between feed pump 3 and preheater 4, through a branch or auxiliary feed pipe I3 provided with a valve I2. If the valve- I in the steam delivery passage 5 is closed, the feed to boiler I by pump 3 is cut ofi by closing valve Na, and the valve I2 in the auxiliary feed pipe I3 is opened. As the boiler is designed for frequent intermittent operation, the valve lid is not closed long enough for all the water to be evaporated from boiler I. During the short period in which valves 1 and Ila, are closed, the excess steam, produced from the water remaining in boiler I by reason of the heat radiating from the grate and the furnace walls, passes through passage 8 into the reservoir 9 and is there condensed by the cold water passing from the spray II). Instead of the spray, or in addition to it, trickling surfaces I4 can also be provided in the steam chamber of reservoir 9.

In order to prevent'container 9 from overflowing on precipitation of the steam, according to the example of Fig. 2 the excess hot water is carried off by an automatic device comprising a discharge valve I6 controlled by a float I5, through a passage-2T, to the feed reservoir 2, preferably through a pipe coil I! provided in the water chamber thereof, so that the heat of the hot precipitated water is recovered.

The embodiment of Fig. 3 includes a circulation boiler with a container or reservoir 9 in which the water separated from the steam generated in tubes I collects and from which the water is again supplied through a pipe I8 to the lower part of boiler I. In normal operation the feed water passes into this separating container 9 from the reservoir 2 through the feed pump 3 through preheater 6 and then passes over a trickling surface I l into the lower part of container 9, passing through pipe I8 to the vaporizer I. In this form the separating container 9 is used at the same time for precipitating the excess steam when the steam delivery is out 01f. A pipe I3 provided with a valve I2 branches from the pressure pipe II of the feed pump 3 in front of the preheater 4, to the spray II] in the steam chamber of container 9. Overflow of container 9 is prevented by the float I5, which in this case correspondingly adjusts a valve I9 in the auxiliary feed pipe I3. In normal operation or the boiler, float I5 should be above the water level in container 9. Thus, a considerable time will elapse before enough water is sprayed into container 9 to raise the water level and the float 9 to close valve I9. During such time the boiler will cool to the point where no appreciable vaporization takes place in boiler I. When the water level in container 9 becomes high enough to close valve I9, there is suffici-ent water in container 9 and boiler I to provide an automatic circulation from boiler I through pipe 5, container 9, pipe I8, to boiler I, and thus prevent the boiler tubes from burning.

Fig. 4 shows another embodiment wherein a certain limited quantity of water is sprayed into the container. This can be done, for example by means of an accumulator, with a compressed air or weight load which has an exactly predetermined water content. In the present example such a collecting receptacle, intended for the reception of a predetermined amount of water, is interposed in the auxiliary passage I3'branching from the preheater 5. This receptacle surface is connected with the steam take-off pipe 5 by means of a pipe 23 provided with a valve 22, while the spacebelow the smaller piston surface is connected by a pipe 24, containing a check or nonreturn valve 28 with the pressure pipe 'II of feed pump 3, and is also connected with the pipe I3 leading to the spray III in the steam chamber of container 9. V

Operationof this apparatus is as follows:

When the main steam valve 1 in the steam take-off pipe 5 and the main feed line II are open, valve 22 in passage 23 is closed, The auxiliary feed pipe I3 is also cut oil. Consequently, the collecting receptacle 20 is charged with cold water by the pump 3 through pipes I I and 24. On the other hand, if the main steam delivery Valve 'I and the feed pipe I I are closed valve 22 in pipe 23 and valve I2 in the auxiliary feed line I3 are opened. As a result of the stepped piston 2| 9, pressure in excess of the boiler pressure is established in receptacle 20, and the water in the latter is sprayed into the steam chamber of container'S by the spray II] through the pipe I3.

In addition to the usual valves provided in the feed lines and necessary for the desired operation, the embodiments illustrated are also provided with an excess pressure or safety valve 25 which, when the'main feed line II is cut off, permits the water which does not 'pass through spray II! to return through a passage 26 into the feed water reservoir 2. In addition, the supply of boiler feedpuinps, particularly when they are constructed as piston pumps, can be cut off by raising the suction valve or brought to a standstill by an independent drive of the feed pump.

The invention can also be utilized where the boiler for constructive reasons has a steam-water drum directly connected therewith.

While We have described herein some embodiments of our invention, we wish it to be understood that we do not intend to limit ourselves thereby except within the scope of the appended claims.

1. A steam generating apparatus for intermittently furnishing steam to a consumer while maintaining a substantially constant boiler pressure during intermittent operation comprising a steam generating boiler of the low water content type, a condensing receptacle of less water content than said boiler, feed water means for said boiler, steam take-off means for said boiler, means forsuddenly closing off said take-off means, means to conduct steam from said boiler to said receptacle, and means for injecting condensing water into the steam in said receptacle during periods of no steam take-off from said boiler.

2. An apparatus as in claim 1, said injecting means comprising water conducting means connecting said feed water means and said receptacle, and means for dispersing said water within said receptacle.

3. An apparatus as in claim 1, a preheater connected to said feed water means, means conducting said feed water into and through said receptacle to said boiler, means connecting said steam take-off means into and through said receptacle, and means connecting said injecting means to said feed water means.

4. A method of operating a steam generatin apparatus composed of a boiler of low water content having a steam condensing receptacle connected thereto, consisting of supplying feed water to said boiler, intermittently withdrawing steam from said boiler with sudden stoppings of the steam withdrawal, and storing said feed water and condensing steam in said receptacle during periods of no steam take-off whereby said boiler is maintained at substantially constant steam pressure.

5. A method as in claim 4 further consisting in feeding said feed water into said receptacle and then to said boiler, and feeding steam generated in said boiler to said receptacle for steam and water separation.

6. A method as in claim 4 further consisting in feeding feed water to a spraying means in said receptacle during periods of no steam take-off.-

7. A steam generating apparatus for intermittently furnishing. steam to a consumer while maintaining a substantially constant boiler pressure during intermittent operation comprising a steam generating boiler of low water content, a condensing receptacle of less water content than said boiler, means for feeding feed water into said receptacle and then to said boiler, means for conducting steam from said boiler to said receptacle, means for conducting steam from said receptacle to a point of use, means for conducting feed water from said feed water means to a spraying device in said receptacle, and means for automatically regulating said water supplied to said device.

8. An apparatus as in claim 7, said automatic means being responsive to the water level in said receptacle.

9. A steam generating device for intermittently furnishing steam to a consumer while maintaining a substantially constant boiler pressure during intermittent operation comprising a steam generating boiler of the low water content type, a condensing receptacle of less water content than said boiler, feed water means for said boiler, steam take-off means for said boiler, means for suddenly closing off said take-off means, means to conduct steam from said boiler to said recep- OTTO H. I-IAR'I'MIANN. RUDOLF LOEWENS'I'EIN. 

